1. Field of the Invention
This invention relates to an acoustic polarimeter for measuring the anisotropy of a solid by determining its acoustic birefringence, the anisotropy being induced by an acoustic stress, for example.
2. Description of the Prior Art
It is known that, if a linearly polarized acoustic wave is applied to the input of an anisotropic solid, the output wave usually has elliptical polarization. This ellipticity depends on the phase shift of the wave between the wave components along the two related orthogonal axes, namely the slow axis and the fast axis. The ellipticity also depends on the angle made by the initial polarization with the slow and fast axes.
A measurement of polarization therefore involves the determination of the slow and fast axes and the phase shift introduced by the solid in respect of the components along these two axes.
It is known to measure with a probe comprising an electroacoustic transducer which transmits the polarized acoustic wave and coupled to a generator for producing electrical signals at a frequency which can be varied either continuously or periodically. The probe being provided in addition with an auxiliary birefringent plate placed behind the emitting transducer and an assembly comprising two electroacoustic transducers which are sensitive respectively to the polarization components located at 45.degree. to each other.
The solid to be measured being introduced between the auxiliary birefringent plate and the assembly of receiving transducers. The probe unit being orientable and the solid-polarization parameters measured by means of signals delivered successively by the two receiving transducers.
The disadvantage attached to the polarimeter in accordance with the prior art lies in the fact that it entails the need for two receiving transducers which cannot be aligned simultaneously with respect to the incident wave; this is liable to give rise to errors in the determination of parameters.